We continue to develop mathematical models of human metabolism and body weight dynamics. We have extended our model of childhood growth to simulate normal development from birth through adulthood as well as the development of childhood obesity. This model is also being applied to better understand growth faltering with malnutrition. We used our model of adult macronutrient metabolism to successfully predict the results of a clinical research study involving the metabolic responses to selective restriction of dietary carbohydrates versus fat in adults with obesity. When simulating what might happen over longer periods, the model predicted relatively small differences in body fat loss with widely varying ratios of carbs to fat. Those results suggest the body may eventually minimize differences in body fat loss when diets have the same number of calories. We validated that our mathematical method provides accurate measurements of calorie intake changes by simply tracking peoples weight. The method was validated using data from 140 men and women who underwent a two-year calorie-restriction intervention. We calculated changes in the number of calories the participants ate throughout the intervention using repeated doses of doubly-labeled water (DLW) and dual energy x-ray absorptiometry (DXA) scans, expensive laboratory techniques not widely available. Using only each persons age, height and sex, and weight measurements gathered throughout the two-year study, we showed that, on average, the model-calculated changes in daily calorie consumption were within 40 calories of the DLW and DXA methods.